1. Field of the Invention
The present invention relates to an image forming apparatus, a control method for the image forming apparatus, and a computer program.
2. Description of the Related Art
In a printing apparatus, job data, including page-description language (PDL) data, is sent from an external apparatus, such as a personal computer (PC), to a rendering unit, where the job data is rasterized into bit map data, and after the bit map data is subjected to color conversion processing in a printer engine, the bit map data is printed onto a medium, such as a sheet of paper. In some printing apparatuses, however, pre-color conversion processing is performed on the bit map data by the rendering unit before it is sent to color conversion processing by the printer engine. The pre-color conversion processing includes pre-color processing, which is performed on color data, and monochrome processing, which is performed on monochrome data. These preliminary types of processing are performed to produce subtle differences in reproduction of, for example, warm-tone black, cold-tone black, and pure black in monochrome processing in the color conversion processing in the printer engine. Warm-tone black is gray added with a shade of red which is reproduced to give a warm impression about black in monochrome processing. Cold-tone black is gray added with a slight blue tone which is reproduced to give a cold impression. Pure black is used as a neutral black.
In the color conversion processing in the printer engine, a color conversion table for color print is used for color data, and a color conversion table for monochrome print is used for monochrome data. In the pre-color conversion processing, pre-color processing is performed on data which is subjected to color-conversion processing for color print in the printer engine unit, and pre-monochrome processing is performed on data which is subjected to color conversion processing for monochrome print.
In an ordinary printing apparatus, if color data and monochrome data are included in rendered bit map data, color data and monochrome data are separated, and color conversion for color is performed on color data, and color conversion for monochrome is performed on monochrome data (Japanese Patent Application Laid-Open No. 10-124276). In such a configuration, color conversion processing needs to be performed by switching between a color conversion table for color and a color conversion table for monochrome.
However, when high-speed printing is performed with the printer engine, color conversion processing by the printer engine needs to be executed at high speed according to the printing speed. When color data and monochrome data are mixed in rendered bit map data, if it is necessary to switch between a color conversion table for color and a color conversion table for monochrome, the color conversion processing sometimes takes too long to be in time for printing.
For example, in two-sided printing or saddle stitch binding, it is necessary to perform imposition in advance while considering layout of pages. As a result of the imposition, monochrome page data and color page data are often included in rendered bit map data. In this case, high-speed printing is unfeasible due to a use of different color conversion tables for color and monochrome. For this reason, in a printing apparatus for high-speed print, when monochrome pages and color pages are mixed in rendered bi-map data, this may be treated as an error and the processing may be suspended.